1.Field of the Invention
The present invention relates to a rotating storage apparatus and information recording method, and in particular, to protective measures against shock and vibration during the operation of information storage apparatus in which information is recorded on a rotating recording medium such as a hard disk.
2.Description of the Background Art
In recent years, information processing systems have been widely used in portable devices such as notebook personal computers. In portable devices, vibration and shock are unavoidable and protective measures against vibration and shock have become important. Improvement of shock resistance is a very important especially in a storage apparatus containing a rotating recording medium such as a hard disk because it has a moving mechanism for changing relative positional relationship between a head having read/write capability and the rotating medium.
As is known to those skilled in the art, tracks are provided on a rotating recording medium (hard disk) in hard disk drive, for example, and a head is positioned over a track to record a magnetic signal from the head in the track. If the head underwent external shock or vibration while the head is positioned over a track and information from the head is being recorded (written) in the track, the head would go off the predetermined track (off-tracking) and the information would be written in a position at a distance from the predetermined track. The information written in such an off-tracking condition may not only cause a read error but also, if information has been recorded in adjacent tracks, affect the adjacent tracks to prevent the information from being recorded correctly.
Examples of approaches for preventing information recording in an off-tracking condition includes a technology described in Published Unexamined Patent Application No. 1-126412(Japan). The technology is described in that application which has the object of improving the performance of a rotating recording apparatus in an environment in which the apparatus undergoes a shock. In particular, the timing control is optimized for a retry operation according to the affecting magnitude of shock force or vibration. An optimum retry interval is set according to the magnitude of the shock or vibration from retry intervals stored in memory to cause a data write operation to be retried with an optimum timing if the shock or vibration is detected to halt the write operation. In this way, the number of retries or wasteful latency could be reduced compared with the case where a fixed retry latency is determined, thereby improving the performance of the apparatus.
However, the technology described in that application and other prior-art technologies have the following problems. A gravitational acceleration sensor (G-sensor) is used to detect a shock and vibration. The physical quantity detected by the G-sensor is acceleration (proportional to force) and does not exactly reflect the off-tracking amount described above. The off-tracking amount is a displacement (position) from an intended track position at which a head is to be positioned. Although a shock or vibration (force) causes the displacement of the head and therefore off-tracking, an output from the G-sensor does not directory represent the off-tracking amount. Because a position is typically represented by the double integral of force in a system in which a feedback is provided, such as the head positioning control system of a hard disc drive, an actual off-tracking amount is provided with time delay with respect to the output of the sensor. As a result, a problem arises if a pulse-like shock that is as short as the time delay is exerted, as described below. This problem will be described with reference to FIG. 6.
FIG. 6A shows a logic circuit diagram for explaining the problem. FIG. 6B shows a diagrammatic drawing. As shown in FIG. 6A, a shock output signal 101 (called a shock out), which is present if an output from the G-sensor exceeds a predetermined threshold, is referenced when a write gate signal 102 is asserted (goes high). When both of the shock out signal 101 and the write gate signal 102 are high, the output of an AND circuit 103 goes high and is latched by a latch circuit 104 for a predetermined time period and a write inhibit signal is generated. The write inhibit signal is inverted by a NOT circuit 105 and input to an AND circuit 106 to mask the write gate signal 102 (force it low). This inhibits the write operation. In other words, the shock out signal 101 is referenced only when the write gate is open and the write inhibit signal is not generated when the write gate is closed (the write gate signal 102 is low).
This will be described in time sequence with reference to FIG. 6B. Curve 110 is a waveform representing, with respect to the time-axis, an output from the G-sensor when a short pulse shock is exerted. The shock out signal 101 is continuously output in the output waveform of curve 110 while a threshold 111 is exceeded. However, unless the write gate signal 102 is asserted (high), no write inhibit signal is generated, as described above. Here, no problem would occur if the phase of the waveform 110 of the sensor output matches that of off-tracking amount at the position of the head. However, an actual off-tracking at the head position is delayed with respect to the sensor output waveform of curve 110 as shown by curve 113. If the write gate signal 102 is asserted (high) at time t2 immediately after the time (t1) at which the shock out signal 101 stops, no write inhibit signal would be generated and a write operation start because the shock out signal 101 is not high even though the head position is off-track.
The inventors of the present invention have found that the above-mentioned problem was likely to arise when a hard disk drive is installed in a portable computer, which in turn is particularly susceptible to an external shock and vibration. Also the problem is more pronounced as the recording density increases. For example, the above-mentioned problem is likely to occur when the storage density is increased to about 30 ktpi or over in a typical hard disk drive of 4,200 rpm.
What is needed is a disk drive with more robust resistance to shock disturbances.